Traveling has always been important for people and there has always existed a need to find destinations smoothly, easily and time efficiently. The demand is emphasized by the enormous success the Global Positioning System (GPS) imply to find a desired destination. The problem with today's global navigation satellite systems (GNSS) is that they only work outdoors and that the destination only can be entered to a building. The reason is that the GNSS satellite signals are weak and cannot enter buildings. When it comes to larger buildings such as airports, university campus, hospitals or shopping malls, the need to find a desired destination within the building remains. A traveler can thus easily find an airport, but does not get any help to find his terminal or gate. To solve this problem and create an overall solution that helps persons to find their desired destination smoothly and easily within a building implies a time saving potential not only for the user but also for the building owner, facility manager, operating body or employee, that does not need to wait for a late person. Further, when first responders are called using mobile phones, the operator will automatically get the caller position using GPS. Since this is not possible indoors, a first responder action sometimes gets delayed due to an uncertain victim position.
U.S. Pat. No. 5,959,575 describes an indoor GPS based navigation method, where ground transceivers transmit pseudo satellite signals in the building. Other solutions are based on radio frequency transmitters, which signals are utilized to triangulate the user's position. All available solutions have in common that they require that the buildings are equipped with some sort of infrastructure (e.g. transmitters) and that these are calibrated manually, which is costly and time consuming. In such solutions, the building structure may be used as a map to exclude impossible motion paths that pass walls and other building structures.
To use the building structure as a map has several disadvantages. The position along a motion track is calculated with an uncertainty. The computed motion track may then look shaky to the user, since the calculated position points seldom resemble a straight line even if the user moves straight ahead most of the time. Further, using dead reckoning supported by a map the position estimate will commonly get stuck in corners or other parts of the building due to heading errors that cause the position estimate to drift off. Further, building maps have no standardized data format in contrast to other geographical information systems (such as street maps, sea charts, elevation maps etc), which uses a vector based format. Further, the building maps require a lot of disk space, since they are normally represented as bit-mapped images. It thereby might become a problem to store the building maps in e.g. a hand held device.
In another solution, the user's position is identified by comparing the signal strength from at least one transmitter received by e.g. a hand held device with a predetermined signal strength map. The production of a signal strength map is time consuming and costly, since the signal strength and the positions at which it is recorded must be determined manually and cover the whole building. Furthermore, if the signal strength is changed, e.g. one transmitter is out of order or it is moved, or e.g. a door is open or closed, the predetermined signal strength map must be recalibrated or it will result in positioning problems.
A method to navigate in an indoor environment, by first manually producing a map model by acquiring physical conditions with passive sensors in a number of known positions, and then measure the same physical conditions at unknown positions and compare with the map model, is presented in U.S. Pat. No. 6,323,807.
Consequently, there is a need for a method of positioning a user inside a building that does not require a time consuming production of a signal strength map or costly additional infrastructure in the building.